Record identifier of LinkageData. It stores the mass properties of the links. Mass properties data consist of a list of {inertiaFrame,mass,momentOfInertia} sublists.
inertiaFrame is a 4X4 homogeneous transformation matrix. The origin of the inertia frame is the center of mass of the link. The moment of Inertia matrix is calculated w.r.t the inertiaFrame.
mass is the mass of the link. The unit of the mass is defined in the $LDMechanismID record.
momentOfInertia is a 3X3 matrix that specifies the moment of inertia of the link w.r.t inertiaFrame.